Multi-chip modules which include a number of integrated circuit chips in a single package play an increasingly important role in the electronics industry. The chips within a module may be functionally equivalent, such as an array of memory chips to provide a capability of forty megabytes. Alternatively, the chips may be functionally related, such as a chip set comprising a read only memory chip, a random access memory chip, a microprocessor and an interface chip.
An important concern in the fabrication of a multi-chip module is the method of electrically connecting the integrated circuit chips to the module. This concern is equally important in connecting chips to other substrates as well. Three well known techniques are commonly referred to as wire bonding, tape automated bonding and surface mounting. The wire bonding method is one in which miniature wires are connected at first ends to input/output pads of an integrated circuit chip. The opposite ends of the bond wires are welded to a substrate, such as a multi-chip module. Wire bonding can be performed with gold wire by thermal compression, ultrasonic or thermal sonic techniques, or with aluminum wire by the ultrasonic technique.
Tape automated bonding involves the formation of a spider-like metal pattern of conductive fingers which radiate outwardly from the integrated circuit chip for attachment to contact sites of a substrate.
Integrated circuit chips may also be fixed to a substrate using a surface mounting method in which solder bumps are formed at the input/output pads of the chip. The chip is placed face down onto the substrate, whereafter the temperature is increased to cause the solder bumps to reflow for direct bonding of the input/output pads of the chip to contact sites on the substrate. This method is sometimes referred to as flip-chip mounting, since the chip is faced downwardly onto the substrate.
Less conventional chip interconnection methods are also known. For example, U.S. Pat. No. 5,065,280 to Karnezos et al. describes a module in which chip interconnect frames are brought into contact with a multi-layer flexible printed circuit board which connects to a motherboard.
While each of the interconnection methods has a number of desirable aspects, as the density of input/output pads of integrated circuit chips increases, precision chip alignment during mounting onto a substrate becomes more critical. The pitch of input/output pads requires a precise alignment to contact sites on a substrate such as a multi-chip module. Even with the use of tape automated bonding frames which have leads that "fanout," the pitch at the outer lead ends may be 4 mil or less.
Moreover, conventional interconnection methods in which input/output pads or leads are permanently attached to contact sites on the substrate render it difficult to repair or replace defective chips. Typically, a single defective chip in a multi-chip module will require the entire module to be discarded.
It is an object of the present invention to provide an electrical assembly in which assembly components can be repeatedly attached and detached without requiring complicated or cost-ineffective techniques.